ABS Compositions and process for preparing same

Abstract

An intermediate for use in a polyblend consisting essentially of a copolymer of monoalkenyl aromatic monomer such as styrene and a ethylenically unsaturated nitrile monomer such as acrylonitrile surface grafted onto rubber which is dispersed in a matrix copolymer of the graft copolymer monomers, the dispersed phase being monomodal in particle size distribution and the weight percent of surface-grafted nitrile monomer being less by at least 2% than the weight percent nitrile monomer in the matrix. This intermediate with mismatched nitrile monomer can be blended with another rubber graft copolymer of different particle size dispersed in ungrafted matrix which contains matched nitrile monomer in the surface graft and matrix to provide a polyblend having properties at least equivalent to those obtained by blending two rubber graft copolymers of different particle size dispersed in a matrix which each contain matched nitrile monomer levels in the surface graft and matrix. The mismatched intermediate is prepared by continuous mass polymerization.

I claim: 
     
       1. An ABS intermediate for use in a polyblend, said intermediate consisting essentially of a copolymer of styrene and acrylonitrile grafted onto a preformed rubber substrate which is dispersed in ungrafted matrix copolymer of styrene and acrylonitrile, said copolymer of the graft and said matrix copolymer each containing 60 to 85 weight styrene and 15 to 40 weight % polymerized acrylonitrile, the weight percent of surface-grafted acrylonitrile in the copolymer being different by at least 2.0% from the weight percent polymerized acrylonitrile in the matrix copolymer. 
     
     
       2. The ABS intermediate of claim 1 wherein the dispersed rubber graft copolymer is monomodal in particle size distribution. 
     
     
       3. The ABS intermediate of claim 1 or 2 wherein the percent surface-grafted acrylonitrile in the rubber graft copolymer is less than the percent polymerized acrylonitrile in the matrix copolymer by about 5 percent. 
     
     
       4. The ABS intermediate of claim 3 wherein the rubber graft copolymer has about 18 to about 25 weight percent surface-grafted acrylonitrile and the matrix copolymer has about 25.5 to about 33 weight percent polymerized acrylonitrile.